Ritodrine hydrochloride is a pharmaceutical active ingredient classified as beta2-adrenergic agonist, used for its tocolytic action.
The chemical name of Ritodrine hydrochloride of formula (A) is 4-((1RS,2SR)-1-hydroxy-2-{[2-(4-hydroxyphenyl)ethyl]amino}propyl)phenol hydrochloride.
Legenda=and Enantiomer    Ritodrine hydrochloride is the racemate of the erythro form.    Ritodrine hydrochloride and its synthesis are described in U.S. Pat. No. 3,410,944. In the examples shown in U.S. Pat. No. 3,410,944, Ritodrine hydrochloride is isolated as a solid having a melting point of 183-186° C. and 193-195° C. Such different melting points are not compatible with a single polymorphic Ritodrine hydrochloride. The crystalline form of a pharmaceutical active ingredient has an impact on its stability, hygroscopicity, solubility, its dissolution speed and its bioavailability. It is therefore fundamentally important to precisely control the crystalline form of the active ingredient and of the methods to obtain it.
A different Ritodrine hydrochloride synthesis process is described in EP0492719 and comprises a non-diastereoselective reduction step with sodium borohydride (NaBH4) that provides an erythro/threo mixture 7.5:1, thus obtaining about 12% of undesired isomer mixture.
EP0603414 describes a stereoselective synthesis for obtaining (−)-Ritodrine hydrochloride and, alternatively, the isolation of (−)-Ritodrine through separation on a chiral column. EP0603414 does not refer to polymorphic forms of the compound.